Post-traumatic perineuraloptic nerve cyst: An incidental rare finding on radiological imaging

A 13-year-old girl presented to an ophthalmology department with a chief complaint of vision loss in the left eye after she suffered trauma with a wooden stick 1.5 months ago. The patient consulted a local ophthalmologist, where she underwent primary lid repair for a wedge-shaped lid tear at the junction of medial one-third and lateral two-thirds of the lower lid in the left eye. On consecutive visits, the patient was diagnosed with post-traumatic optic neuropathy with vitreous hemorrhage, for which the patient was given intravenous 1 g methylprednisolone for 3 consecutive days, followed by oral steroids (1 mg/kg body weight) for 11 days. However, there was no improvement in the visual acuity. On examination, visual acuity was 20/20 in the right eye, and no perception of light in the left eye. There was the presence of grade 3 relative afferent pupillary defect (RAPD) in the left eye. Slit-lamp evaluation of the right eye was normal. However, the left eye showed the presence of red blood cells (RBCs) in the anterior chamber, posterior subcapsular cataract (PSC), and retrolental RBCs. There was a media haze of grade 3 on fundus evaluation of the left eye. Therefore, left eye B scan ultrasonography was done, which showed the presence of vitreous hemorrhage and a well-defined, thin-walled cystic lesion through transmission attached to the anterior intra-orbital part of the optic nerve [Figure 1]. MRI was suggestive of a perineural cyst at the left optic nerve head (4 × 2.5 mm) lateral to the optic nerve, likely post-traumatic with the edematous appearance of the proximal intraconal optic nerve early disc edema with vitreous hemorrhage [Figure 2]. A neurosurgery opinion was sought for the same. However, no active surgical intervention was done because of poor visual prognosis in the left eye due to time-lapse.Figure 1: The axial B scan (a) and color doppler (b) images of the left eye show a small anechoic avascular cystic lesion (arrowhead) with posterior acoustic enhancement along the lateral aspect of the retro-orbital portion of the optic nerve head (black arrow). Also seen are coarse internal echoes (long white arrows) within the vitreous suggestive of vitreous hemorrhageFigure 2: The axial (a), coronal (b), and oblique sagittal (c) heavily T2-weighted MR images of orbit show a small eccentrically located cyst at the left superolateral aspect of the intra-orbital portion of the left optic nerve (white arrow) immediately behind the globe, suggestive of a perineural cyst. Note the subtle T2 hyperintensity on the retro-orbital part of the left optic nerve (dashed white arrow). The left optic nerve appears edematous with effacement of peri-optic CSF space, better visualized by comparing the normal-appearing right optic nerveDiscussion Orbital injuries are nowadays quite common and can have a varied presentation. An optic nerve cyst, whether spontaneous or congenital, is a rare clinical entity.[1,2] Multiple etiologies have been described for the formation of optic nerve cysts. It includes arachnoid cysts, post-traumatic or postoperative cysts, neuroepithelial cysts, congenital cystic eye or microphthalmos with cysts involving the optic nerve, idiopathic causes, associations with meningiomas and meningocele.[3,4,5] However, the development of post-traumatic perineural cysts lateral to the optic nerve after blunt trauma is rare. In our case, magnetic resonance imaging (MRI) was consistent with an arachnoid cyst of the optic nerve. There was no associated orbital wall fracture. Hence, it might be possible that entrapment of neuroepithelial cells during trauma might have led to cyst formation, or might be a loculated Cerebrospinal fluid (CSF) surrounded by fibrous proliferation as proposed by Akor et al.[5] Our case is unique as it highlights the importance of radiological imaging as the timely multidisciplinary approach may be amenable to visual rehabilitation. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.